In recent years there has been unusual interest in providing more accurate, versatile and easily operated equipment and techniques for cutting metal plate and pipe with both simple and complex predetermined contours for many reasons including the many improvements which have been made in forming welded joints. To meet these demands designers have made many proposals for cutting metal to shape utilizing hot cutting jets. However, such proposals are subject to many shortcomings and disadvantages not satisfactorily avoided prior to the present invention. The problems have been particularly serious as designed for cutting thick workpieces including pipe used to form high-strength structures as, for example, submerged well drilling and producing platform and similar structures utilizing tubing of widely varying diameters and thicknesses welded together in an endless variety of patterns and arrangements. The great majority of the joints between components are of an endless non-standard variety which it is impractical to cut utilizing previously proposed mechanical contour generating equipment.
Typical prior art jet cutting devices for cutting metal are disclosed in Arnault et al. U.S. Pat. No. 3,084,923; Steventon et al. U.S. Pat. No. 3,153,109; Grubish U.S. Pat. No. 3,206,180; Lyons U.S. Pat. No. 3,228,671; Powers U.S. Pat. No. 3,330,547; Selkirk U.S. Pat. No. 3,552,731; Waldron U.S. Pat. No. 3,790,144; Hiratska U.S. Pat. No. 3,362,699; Redman U.S. Pat. No. 3,398,342; Usami U.S. Pat. No. 3,492,551; Inomata U.S. Pat. No. 3,819,162; Sekine et al. U.S. Pat. No. 3,843,103; Blackburn U.S. Pat. No. 3,430,938; Blackburn U.S. Pat. No. 3,614,077; Hooper U.S. Pat. No. 3,866,892; and Marshall U.S. Pat. No. 3,936,714.
Steventon et al. discloses a tape controlled cutter suitable only for plate stock cut along X and Y axes and lacking provision for cutting a bevel edge so important when torch-cut parts are to be welded together. The Grubish cutter is designed to cut pipe while rotated in a clamping buck and utilizing mechanical linkages the adjustment of which for each cut is difficult and time consuming to make and involving trial and error manipulations to check the correctness of each new setting. Powers, Selkirk and Waldron show various cutting devices of the tracer-controlled type wherein a different master is required to control travel of the cutting jet for each pattern to be cut. Hiratska proposes a cutter utilizing an analog electro-mechanical control incorporating a multiplicity of manually adjustable potentiometers and requiring a special control circuit for complex and nonstandard cuts. The pipe must be clamped in a rotating chuck while being cut and the cutting jet is preset at a selected angle at the outer end of a support rotating about a radial axis of the pipe undergoing cutting. This equipment is therefore limited to cutting holes in the sidewall of pipe since the bevel angle so important in making welded joints cannot be controlled properly. Usami and Lyons propose a three axis tape controlled metal cutter but each device is seriously limited by the fact that the cutting can be jet rotated only about an axis normal to the workpiece. Hopper's tape-controlled cutter lacks any provision for making bevel cuts. The three axis flame cutter of Inomata is specially designed for the final size-cutting of curved plates of variable thickness, such as the curved components of ship hulls, utilizing plural sensors in contact with the hull surface. The hull component undergoing cutting remains stationary and the cutting equipment is moved bodily while the several sub-assembly components of the apparatus are moved independently and relative to the component being cut. Sekine et al. also deals with the problem of bevel cutting of both plate stock and layered ship hull components of varying thickness in such manner as to maintain the remote bevel edge in a straight line as well as to regulate the spacing of the torch from the stock. His equipment lacks means for varying the bevel angle without departure from a desired predetermined remote-side contour as well as means for tilting the cutting torch about an axis tangent to this predetermined remote-side contour. His torch positioning means requires sensing rollers in contact with the opposite sides of the workpiece and this is obviously impractical in cutting large stock and long pipe. The two Blackburn patents disclose three axis pipe cutters each using a manually settable mechanical linkage in combination with eccentrics to control and generate each cutting pattern of the cutting torch. Marshall's flame cutting apparatus is controlled by a pair of optical scanners which follow the respective front and rear traces of the cut to be made, the traces being mounted on a drum rotating in timed relation to the rotation of the pipe being cut. His system is constructed and controlled in accordance with quite different principles requiring accurate determination of the tangent of the bevel being cut axially of the pipe at each circumferential increment about the girth of the pipe. He further requires two feed back loops as well as a circumferential scan line around the pipe, all cooperating to compensate for creep. Additionally, he has no provision for maintaining the torch at a predetermined distance from the surface of the pipe to compensate for out-of-roundness so commonplace in large diameter pipe.